Typically, during processing a device which prints a circuit on a semiconductor wafer, the back side of the semiconductor wafer is held by a vacuum chuck, and the front side is polished. The yield rate is decreased because the unevenness of the back side, which is chucked, influences the front side in the processing device. To solve this reduction in yield, the back side must also be polished. As such, both the front and back sides of the semiconductor wafers are simultaneously polished by using a double sided polishing apparatus.
However, problems often occur in the device process. For example, when the semiconductor wafer is polished on both the front and back sides, it becomes very difficult to distinguish the front from back side by visual inspection and sensors which are used to convey and position the wafer.
In JP 6-349795, a method of making semiconductor wafers is disclosed. The method maintains the yield rate during the circuit print of the device process, and the method prevents the problem of distinguishing the front from back sides of the wafer.
In the JP 6-349795 method, a sliced wafer 6 is chamfered (FIG. 6(a)); the sliced surface 61 is flattened by lapping (FIG. 6(b)); the lapped wafer 6 is etched with alkaline solution (FIG. 6(c)); and the back side of wafer 6 is polished to remove most of the unevenness 64 which is formed by the alkaline etching. (FIG. 6(d))
Metal pollution is more difficult to remove from an alkaline etching solution than from an acid etching solution. If the metal radicals of the alkaline solution, such as potassium hydroxide (KOH) or sodium hydroxide (NaOH), remain in the etching solution, these metallic radicals will also constitute part of the metal pollution.
In this method, since the wafers are necessarily polished in side by side processes, the manufacturing efficiency is not optimized. When using a polishing block to polish the wafers, processes are required to adhere and remove the wafers from the polishing block. In this method, not only are the processes increased, but many chemicals are required to clean the wafers and the blocks.